docs: def mask_reduce(mask):
      """Reduce a boolean mask, removing all false slices in any dimension.
  
      Parameters
      ----------
      mask : ndarray with bool dtype
          The mask which is to be reduced
  
      Returns
      -------
          A boolean mask with no all False slices.
      """
      mask = mask.copy()
      for i in range(len(mask.shape)):
          a = mask.copy()
          j = list(range(len(mask.shape)))
          j.remove(i)
          j = tuple(j)
          a = a.max(axis=j, keepdims=True)
          idx = [slice(None)] * len(mask.shape)
          a = a.flatten()
          idx[i] = [k for k in range(len(a)) if a[k]]
          mask = mask[tuple(idx)]
      return mask